1. Field
Apparatuses and methods consistent with exemplary embodiments relate to medical equipment, and more particularly, to automatic planning of views in three-dimensional (3D) images of a brain.
2. Description of the Related Art
Medical images acquired by a medical imaging technique, e.g., magnetic resonance tomography (MRT), are widely used in modern diagnostic researches, particularly in researches of a human brain. Qualitative planning of views, also known as planning of scans, has higher importance for visualization of images of an object and correcting diagnosis settings.
Anatomical structures needs to be considered for planning views, i.e., the planned views needs be provided according to anatomical criteria including, for example, existing reference lines, axes and symmetry planes. In particular, in brain researches, standard positions in a plane dividing two hemispheres (i.e., passing through a longitudinal cleft of the brain, also called a longitudinal fissure) are used for a sagittal view, and various standard axial (or transverse) views constructed on stipulated anatomical points are used as a longitudinal plane of symmetry. For example, the standard axial views may be construed according to orientation in Talairach's space.
A procedure of planning of views of a brain may require significant time when manually executed. Planning of views refers to generation of an image having a predetermined cross-section based on a 3D scout image. Moreover, in manual planning, highly qualified medical personnel may spend significant time and energy in a routine operation for performing manual planning. Efficiency of a brain scan may be increased by applying an automatic procedure of planning of views based on the analysis of 3D scout images. Hereinafter, a scout image is understood as a preliminary 3D picture provided for the purpose of localization of area of interest.
Requirements for planning of views for medical images using standard anatomical landmarks, reference lines, and symmetry planes are well known.
Thus, methods of automatic planning of views have been developed. It is desirable that methods of automatic planning of views are performed at a higher speed and reliable (or robust) for use of scout images of lower resolution because the scout images may be often obtained at a preliminary stage together with a view of process acceleration. Much research has been conducted to solve the above task. In general, a mid-sagittal plane (MSP) is used as a natural plane of symmetry and for creating a longitudinal reference axis, which provide anatomical landmarks for this plane. In this regard, most approaches are similar to each other, with differences in methods of searching for reference lines and planes.
Some methods provide aspects related to specific parts of planning of views. For example, U.S. Pat. No. 7,450,983 describes determination of anatomical structures of a brain as connection of anterior and posterior commissures in mid-sagittal planes (MSPs); U.S. Pat. No. 7,986,823 describes determination of an MSP as a separate task; and U.S. Pat. Nos. 8,002,019, 8,190,232 and 8,270,698 also discuss construction of an MSP and search of anatomical landmarks therein.
U.S. Pat. Nos. 7,450,983 and 8,002,019 describe a faster and economical method for searching reference lines to construct an MSP, in which two reference lines detected in sections are used for MSP construction. Such an approach does not show a higher robustness since the method does not process a redundant set of sections. Furthermore, use of lower resolution scout images may lead to unreliable construction of an MSP because of statistical instability of the used data.
U.S. Pat. No. 8,270,698 presents a method of processing of a redundant set of axial sections for MSP construction, which may significantly increase robustness of the method. However, this method uses only axial sections without considering a coronal section. Hence, useful additional information on the coronal section is not used in this method. That is, in this method, working sections are selected without using anatomical features of a brain, and thus, a set of working sections is obtained by simple uniform “chopping” of the whole image from the bottom to the top. Thus, in this method, no preliminary stage of a process for efficient selection of working sections is provided. Robustness of the approach may be increased if processing of coronal sections along with axial sections is provided and a specific procedure implementing a preliminary selection of working sections takes into consideration anatomical features of a brain. There is no preliminary selection of sections in the approach presented by U.S. Pat. No. 7,986,823, which uses only two working sections: a first section (or axial cut) is selected simply as an average layer of the whole 3D scout image.
In U.S. Pat. Nos. 7,450,983 and 8,270,698, an approximate ellipse is constructed and its properties of symmetry are used in processing of sections for detection of a middle line therein. In U.S. Pat. No. 8,270,698, an elliptical mask of a section is constructed by preliminarily selected contour of an image of a brain. The approach is more reliable in which a mask covering the real form of a cut of a brain in a section is used instead of an ellipse encircling a contour. Major axes of such a plane figure may differ from axes of a contour ellipse. Furthermore, at lower resolution of a scout image, a construction of the plane figure covering a section is more statistically reliable than selection of a contour of the section and construction of an ellipse on the contour.
U.S. Pat. Nos. 8,002,019 and 8,190,232 relate to detection of a middle line in sections. Lines of symmetry of approximate ellipses are used only at an initial stage, and detailed stages are applied during which a position of a dark line dividing cerebral hemispheres is detected. Gradient masks are used to detect dark pixels. However, in a real embodiment, detection may be complicated because a desired line may have rather complex properties. The complexity of detection depends on the position of a selected section relative to an anatomical structure of the whole brain and quality of the scout image. For example, the detected line may be discontinuous, non-uniform in intensity of pixels, and have distributed characteristics, which means that the detected line has complicated properties than when a detected local gradient mask is concentrated.
A special numerical criterion for detecting a trace of a longitudinal cleft of a brain (or fissure) in a set area of a section may be used to improve effectiveness of the method. In a certain case, a line that divides cerebral hemispheres may be darker; however, other variants of intensity of pixels that cause such a dark line may exist. For example, the variants of intensity of pixels may depend on a method or protocol used for reception of an image.
In U.S. Pat. Nos. 7,450,983, 8,002,019 and 8,190,232, since only two reference lines are used for construction of an MSP, a post-processing for filtration of the unreliable (or untenable) data is not applied. In the Patent [5], redundant data are used, and consequently the MSP is constructed using a regressive method (i.e., auxiliary reference points are created based on received reference lines, and the required plane is constructed on a set of the points). This approach may increase robustness, but a post-processing for filtration of statistically unreliable reference lines is not applied.
Filtering statistically unreliable reference lines demonstrates a higher reliability. For example, it is possible to delete lines whose direction vector significantly differs from a generalized direction of the whole set of reference lines.